The specification relates to the field of scintillator materials, potentially for use in radiation detectors.
Scintillator materials are used to detect and to measure the energy of ionizing radiation. They are mounted in systems that comprise the scintillator (often a hygroscopic crystal), a housing which may especially be made of aluminum. One of the faces of the crystal is coupled to a photodetector by direct coupling or prior coupling of a glass window which is then coupled to the photodetector. Any coupling may be carried out by a grease or an adhesive, of silicone or epoxy type. The greater the amount of light reaching the photodetector, the better the performance is from the point of view of the energy resolution and the detection threshold, and the less sensitive the photodetector needs to be. The scintillator is usually covered with a reflecting material that scatters the light (polytetrafluoroethylene (PTFE) film, for example) in order to reflect the scintillator the light that tends to exit via its faces covered with said reflecting material. The light can therefore only exit via the face that is not covered and that is coupled to the photodetector, wherein the photodetector then collects the light. Detectors that are thus equipped, in particular photodetectors having rare-earth halide single crystals, are particularly suitable for the identification and characterization (energy, flux, chronometry) of ionizing radiation.
Ionizing-radiation detectors are also used for carrying out imaging, for example, in the case of gamma cameras. Overall, they function along the same principles; however, a ionizing-radiation detector should forego collecting the light that escapes via the side faces since this light amplifies the distortion of the image (deformation phenomenon) and degrades the spatial resolution (blurredness phenomenon).
In order to eliminate this light that is at first misdirected within the scintillator, instead of providing the scintillator with a reflecting material, its lateral faces are covered with an absorbing material that is as black as possible. The face opposite the one that is in front of the photodetector may remain covered with a back-scattering material (such as PTFE). To achieve this absorption of the light on the lateral faces, there are a priori the following alternatives:                a) adhere a black material such as paper or a strip of plastic to the faces of the scintillator; and        b) do not cover the faces of the crystal, but use a housing that has been colored black on the inside, for example by using a black anodized housing.        
The attempts at solutions have a significant drawback: the light is not absorbed immediately on the surface of the crystal but after the adhesive material in case a), and inside the housing in case b). This leads to an incomplete absorption of the light and some of this light may, after all, diffuse into the crystal.